The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
In cellular networks, mobile user devices (e.g., cellular telephones) typically perform an initial “cell selection” process to identify and select a cell having a base station that is capable of adequately serving the user device. Because user devices typically move from area to area, however, the base stations of different cells may become better positioned to communicate with the user devices at different times. Thus, in order to retain a high quality of service, cellular networks typically provide a mechanism for switching which cell serves a user device. When a user device is in active communication with a base station of a serving cell, the process of switching cells is typically referred to as “cell handover”. When a user device is in an idle mode (e.g., in a mode in which only overhead data such as paging messages, broadcast parameters, etc., is received from a base station of a serving cell), however, the process is typically referred to as “cell reselection”. While cell handover is generally instructed by the network, cell reselection is generally determined by the user device.
In some cellular networks, such as cellular networks arranged according to the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) Specification, various cells are grouped into logical units known as “tracking areas”. Under the 3GPP LTE Specification, for example, a user device in idle mode will be sent the same type of paging messages (e.g., paging messages of the same format, and/or paging messages sent at the same interval) so long as the user device remains within a single tracking area. Paging messages are used to notify a user device of emergency information or the arrival of other data intended for the user device, in which case the user device initiates an active communication link with the base station of the cell currently serving the user device. In order to ensure that such paging messages are not lost, a user device in idle mode typically transmits a tracking area update when the user device selects a cell in a new tracking area.
In some systems, a user device can somewhat rapidly change or “ping pong” between cells associated with different tracking areas. For example, a user device in idle mode that follows a meandering path might ping pong between cells of different tracking areas. Even a user device following a relatively straight path near a border of cells in different tracking areas might ping pong between the neighboring cells, e.g. as a result of differing propagation characteristics of communication channels used in the cells. Where the propagation characteristics of the communication channels vary over time, even stationary user devices may be subject to the ping pong effect. Moreover, because each change from one tracking area to another tracking area is generally accompanied by the transmission of a tracking area update from the user device, such scenarios can lead to a heavy signaling load, and increase the risk of losing messages (e.g., paging messages) intended for the user device.